Reduction rims in San Carlos olivines: an analog to reduction rims in ureilite olivines.

1 Introduction

Ureilites are achondrites that contain about 70 vol. % magnesium rich olivine (Fo76-92) and 30 vol. % pyroxene (orthopyroxene as well as clinopyroxene) as main components (Grady et al., 1985). The intergranular matrix contains 3 wt% carbon in the form of graphite and/or diamond veins. Diamond veins, in particular, are important because they are a sign of some high pressure event in the ureilite's development history. As suggested by Takeda (1987) ureilites formed as asteroidal mantle restites with an oxygen-isotopic diversity (Clayton & Mayeda, 1988) suggesting a heterogenous starting material, contrary to the homogenous igneous body theory proposed by Goodrich et al. (1987) and others.....